The Exposure Assessment Core in the new Center will be focused on the analytical chemistry needs and physiologically based toxicokinetic (PBTK) modeling. During the first Center (1998-2003), appropriate collection and handling of field samples (house dust, car dust, and urine) for pesticide analysis was critical for the CIP project. Since field researchers have now been trained and have trained others in these procedures, the emphasis in the new Center will be on providing analytical support for field samples collected by the Community Based Participatory Research Project and the Pesticide Pathways Projects. In first funding cycle of the Center, kinetic modeling also proved invaluable for understanding and translating information on molecular mechanisms and genetic susceptibility. Thus, these areas have been prioritized for the new Center. The Exposure Assessment Core of the University of Washington Center for Child Environmental Health Risks Research has had the following specific aims: Specific aim 1: Provide analytical chemical support to the Community-Based Participatory Research (CBPR) Project and the Pesticide Pathways Project Analyses of house dust, vehicle dust, and urine from adults and children will include organophosphate (OPs) pesticides and metabolites from over 200 households. Specific aim 2: Provide assistance with the interpretation of exposure data to the Community-Based Participatory Research (CBPR) Project and the Pesticide Pathways Project. Interpretation of the results from the house dust, vehicle dust, and urinary analyses is not a straightforward process due to the complex relationship between environmental samples and urinary metabolites. Specific aim 3: Coordinate mechanistic modeling of exposure and dose among all Center projects to be linked with dynamic modeling performed by the Risk Characterization Core. Stochastic models will be generated to explore links between measured environmental pesticide levels and biomonitoring results and ultimately to biological effects. This will require mathematical representation of human behaviors, chemical transfer and absorption processes, and the pharmacokinetics of metabolism and excretion. Exposure and pharmacokinetic models with then be linked with biologically based dose response models to better explore exposure response relationships.